In the mounting of semiconductor chips, it is known to provide the surface of the semiconductor chips with solder, in order to mount the semiconductor chips on a substrate and connect them in an electrically conducting manner by means of this solder.
An electrically conducting connection is produced between a contact point on the surface of the semiconductor chip and a corresponding contact point on the substrate. Since the contact points on the substrate are generally located at a different position than the contact points on the surface of the semiconductor chip, redistribution lines are provided between the contact points on the surface of the semiconductor chip and contact points on the semiconductor chip that correspond to the contact points on the substrate.
As described for example in German Patent Application DE 102 58 081 A1, the redistribution lines are produced from an electrically conductive layer, known as a redistribution layer. In this case, a sacrificial layer, known as a seed layer, is first applied to the entire semiconductor surface. Then a mask, which has mask openings at the points that are intended later to receive the redistribution lines, is applied to the seed layer. By means of an electrolytic process, the metal of the redistribution lines is then deposited in the mask openings. In particular electrostatic potential is applied to the seed layer. In this process, a copper layer is first deposited. The surface of this copper layer is passivated by a nickel layer. Since this nickel layer represents a poor adhesive base for the solder, the surface of the nickel layer is subsequently provided with a gold layer.
The gold layer on the redistribution layer is then possibly partially removed again in a further photolithographic process at the points at which the redistribution layer is not wetted with solder.
In order to prevent uncontrolled flowing away of solder in further process steps, a layer of a solder resist is subsequently deposited over the entire surface. At the points at which the solder is then to be applied, the layer of solder resist is then opened by means of a photolithographic process. In these openings, a flux is then deposited and solder balls are applied. The solder balls are then melted on the redistribution layer by means of a melting process.
A disadvantage of this method is that additional laborious process steps, such as coating, exposing, developing and curing, are required for the creation of the solder resist mask, with the effect of increasing production expenditure.